1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) meter apparatus for displaying a dial plate and a pointer in an analog manner.
2. Description of Related Art
It is believed that a liquid crystal display (LCD) panel has a response speed slower than a CRT and has a difference about times to display a bright color and a dark color.
FIG. 9 illustrates the response speed of a general LCD panel. When the LCD panel displays an image moving faster than the response speed of the LCD panel, a following image is displayed on the LCD panel prior to disappearance of the previous image so that both images appear at the same time in the LCD panel. As shown in FIG. 9, a rise time T1 from the minimum luminance (black) to the maximum luminance (white) is different from a fall time T2 from the maximum luminance to the minimum luminance. The difference of the response speed responsive to the colors results in the several appearances and disappearances of the images.
The LCD panel is utilized for a speed meter of a vehicle or an LCD meter. The LCD meter displays a still image of a circular dial plate and a moving image of a pointer, which rotates and points in the dial plate responding to a running state of the vehicle. The moving image of the pointer is changed every T0 (= 1/60 secs) in the display according to a sampling data of a period of time T0.
FIG. 10 shows a flowchart of processing the moving image of the pointer of a conventional LCD meter. At step S11, a rotation angle responsive to a speed signal is acquired. At step S12, a coordinate of the image on the LCD panel responsive to the rotation angle is calculated. At step S13, an image data of the pointer responsive to the coordination is read from a memory. At step S14, the image data from the memory is displayed on the LCD panel.
The LCD panel is utilized for the meter such as the speed meter of the vehicle. However, when the pointer is moved faster than the response speed of the LCD panel, a last image of the pointer appears on a latest image thereof prior to disappearance of the last image.
As shown in FIG. 11, when the LCD panel starts to display the latest image and at the same time to erase the last image, the last image remains with the latest image. An image density on the LCD panel is always constant (100%).
In this case, as shown in FIG. 12, both the last and latest images G12 and G13 of the pointers appear on the LCD panel. A second last image G11 happens to appear depending on the response speed of the LCD panel so that the plurality of the pointers appear and cause difficulty to identify the instant pointer. The arrows of FIG. 12 only illustrates a rotation direction of the pointer and are not shown in the real display.
JP,2001-117074 discloses a driving method of an LCD panel to solve the problem. The driving method includes a frame memory device for delaying one frame of a first image data inputted from an external apparatus, a calculating device for comparing the first image data with a second image data stored in the frame memory with one frame delayed, and an adjusting device for adjusting corrected data outputted from the calculating device to the first image data. The driving method adds the corrected data to the image data, which changes the state of the image, to speed up the response speed of the LCD panel.
The conventional method corrects the characteristics of the LCD panel to achieve a high speed response with a hardware. When the display panel driven is changed, it is required to change the correction method and the circuit. The conventional method is not versatile.